When a hem is formed at the edge of a piece of a garment such as a sleeve, the raw edge of the material is typically folded underneath the remainder of the material and then sewn with a coverstitch. If the folded edge does not conform to a straight line along the length of the piece as it travels through the sewing machine, the coverstitch will not cover all of the raw edge of the folded under portion of the material. If the raw edge extends for any significant distance beyond the stitching, the sewn product may be rejected by the buyer for poor quality.
The raw edge of sleeves can deviate from the optimally straight fold line for several reasons; e.g., the goods received for sewing were simply not cut on a straight line. With manual pattern making and cutting of goods there is always the possibility of error between the marking operation and the cutting. In highly automated environments with patterns that are produced by CAD systems and that are automatically fed to computer controlled cutting machines, there is a much greater degree of accuracy but the attendant costs make this technology unavailable to vast numbers of garment manufacturers.
The other reasons for deviation from the optimal fold line relate to the method of making the fold. The least effective way of making the fold is to have the sewing machine operator manually fold the piece prior to sewing. This method leads to second quality goods and is usually too slow to be commercially feasible. Another way to make the fold is through a former. Typically, formers have plates which form a channel which progressively inverts the edge of the material as the material is moved through the channel towards the sewing machine. To obtain a uniform hem these formers rely on the operator's skill and close attention in directing the cloth through the former and in maintaining proper alignment of the material throughout sewing. Formers have also been provided which use jets of air to urge materials into the channels for folding. A problem with air jets is that the air from the jets can cause the raw edge to flutter which can cause the edge to lose its alignment with the fold line.
In order to reduce the problems with sewing machine operator error and cutting inaccuracies, conveying systems with edge trimmers have been used. The conveyor systems include conveyors, edge trimmers, formers, and sometimes air jets. In the typical conveyor operation, the sleeve goes through an edge trimming knife and then is immediately captured by a conveyor to maintain the straight edge cut by the knife. The piece is then conveyed by positive traction through a former which creates the fold for sewing. After the piece leaves the former it is fed into the feed dog of the sewing machine. In order to allow for edge trimming, some manufacturers that use the conveying systems require that the pieces be cut with up to a quarter of an inch of extra material at the edge. In the conveying systems, the piece of material is fixed into a specific orientation as it leaves the edge trimmer, and the conveyor does not allow the piece of material to move in any direction other than in a straight line to the sewing head. The formers typically extend to a point very close to the sewing machine in an attempt to maintain control of the edge and the fold for as long as possible before the piece of material engages with the sewing machine.
The conveying systems have not been altogether satisfactory for certain garment manufacturers because of the equipment cost, the added material costs associated with edge trimming and the time and expense of training the operators and service technicians on how to use and service the machines.
What is needed is a hem folding attachment that solves the problems associated with hemming imprecisely cut materials and that solves the problems associated with the manual and automatic hemming methods described above.